On-board fuel desulfurization unit

ABSTRACT

A method for regenerating at least one impurity-adsorbing sorbent bed includes passing impurity-containing fluid through the impurity-adsorbing bed. The impurity-adsorbing sorbent bed adsorbs an impurity in the impurity-containing fluid to produce a purified fluid. A portion of the purified fluid is sent back through the impurity-adsorbing sorbent bed that contains the adsorbed impurity. The impurity-adsorbing sorbent bed is exposed to microwave energy to desorb the impurity adsorbed on the impurity-adsorbing sorbent bed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a divisional of U.S. patent application Ser. No. 11/387,430, entitled “ON-BOARD FUEL DESULFURIZATION UNIT,” filed Mar. 23, 2006 by Thomas H. Vanderspurt et al., which claims the benefit of U.S. provisional application 60/753,860, filed Dec. 23, 2005. The disclosure of U.S. patent application Ser. No. 11/387,430 is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of purification systems. In particular, the invention relates to athermal desulfurization systems.

Most hydrocarbon or biomass derived fuels contain sulfur in excess of the level tolerable by fuel cell systems without loss in performance. This is particularly true of on-board fuel cell systems used as auxiliary power units. Most fuel cells typically give the best performance using pure hydrogen. Even a small percentage of sulfur (in the parts per million range) in the fuel gas can severely degrade the performance of the fuel cell. Solid oxide fuel cells, however, do not require pure hydrogen to operate. Solid oxide fuel cells are capable of operating on hydrocarbon fuels that produce carbon monoxide, which acts as a fuel to the electrodes in the fuel cells. While solid oxide fuel cells can run on fuel that contains hydrocarbons, the fuel must still be generally free of other contaminants, such as sulfur.

There are numerous mechanisms known in the art for removing sulfur from fuel. It is well known that certain high surface area solids can adsorb or chemisorb sulfur-containing molecules typically found in fuel including mercaptans, sulfides, thiophenes, thiophanes, and the like. Thus, one method currently being used to remove sulfur from fuel is to pass the sulfur-containing fuel through a sorbent bed. The sorbent bed adsorbs the sulfur from the fuel, resulting in a fuel that is either sulfur-free, or containing only a nominal amount of sulfur. However, sorbent beds can only adsorb a specified amount of sulfur before reaching a breakthrough point, at which time the sulfur begins to pass through the sorbent bed, making the sorbent bed less effective. Once the sorbent bed reaches the breakthrough point, it must be regenerated prior to reuse.

One of the methods currently being used to regenerate sorbent beds is to apply thermal energy to the sorbent bed in the presence of a flowing fluid in order to excite, desorb, and remove the sulfur-containing molecules from the sorbent bed. The sorbent bed is first heated to desorb the sulfur from the sorbent. After the sorbent bed has cooled down, it can be used to adsorb additional sulfur compounds. Thus, a heat exchanger is typically needed to regenerate the sorbent bed. Due to the need for high thermal energy and a bulky heat exchanger to regenerate the sorbent bed, it is often impractical to have a sorbent bed regeneration system on-board a moving vehicle, such as a jetliner or a truck. Additionally, the use of high thermal energy can often reduce the overall efficiency of the sorbent bed or significantly limit the life of the sorbent.

BRIEF SUMMARY OF THE INVENTION

A method for regenerating at least one impurity-adsorbing sorbent bed includes passing impurity-containing fluid through the impurity-adsorbing bed. The impurity-adsorbing sorbent bed adsorbs an impurity in the impurity-containing fluid to produce a purified fluid. A portion of the purified fluid is sent back through the impurity-adsorbing sorbent bed that contains the adsorbed impurity. The impurity-adsorbing sorbent bed is exposed to microwave energy to desorb the impurity adsorbed on the impurity-adsorbing sorbent bed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first embodiment of a sorbent bed regeneration system.

FIG. 2A is a graph of the capacity of a sorbent bed of the first embodiment of the regeneration system at an initial breakthrough point.

FIG. 2B is a graph of the capacity of the sorbent bed of the first embodiment of the regeneration system at a breakthrough point after the sorbent bed has been regenerated.

FIG. 3A is a schematic diagram of a second embodiment of a regeneration system having multiple sorbent beds at an initial time.

FIG. 3B is a schematic diagram of the second embodiment of the regeneration system when a first sorbent bed has reached its breakthrough point.

FIG. 3C is a schematic diagram of the second embodiment of the regeneration system when a second sorbent bed has reached its breakthrough point.

FIG. 4A is a schematic diagram of the second embodiment of the regeneration system using reverse flow regeneration at an initial time.

FIG. 4B is a schematic diagram of the second embodiment of the regeneration system using reverse flow regeneration when the first sorbent bed has reached its breakthrough point.

FIG. 4C is a schematic diagram of the second embodiment of the regeneration system using reverse flow regeneration when the second sorbent bed has reached its breakthrough point.

DETAILED DESCRIPTION

FIG. 1 shows a schematic diagram of athermal, on-board sorbent bed regeneration system 10 that removes impurities, such as sulfur, from a fluid using a sorbent bed and then regenerates the sorbent bed. Regeneration system 10 is a multibed system with recycle and generally includes circulation system 12, raw feed tank 14, desulfurizer feed pump 16, first sulfur sorbent bed 18 a and second sulfur sorbent bed 18 b, purified product tank 20, purified product pump 22, reformer 24, desulfurizer recycle pump 26, microwave energy source 28, and effluent tank 30. Regeneration system 10 also includes a plurality of valves: first raw feed valve 32 a, second raw feed valve 32 b, first output valve 34 a, second output valve 34 b, first reverse flow valve 36 a, second reverse flow valve 36 b, first effluent valve 38 a, and second effluent valve 38 b. All of the valves are switchable between an open position and a closed position. In the open position, the valve allows fluid to flow through the valve. In the closed position, the valve prevents fluid from flowing through the valve. Regeneration system 10 is designed using actuated valves to connect multiple sorbent beds head to tail to form a circle where each bed is also connected to the feed line, the product line, and the concentrate line.

Due to its ability to athermally regenerate first and second sulfur sorbent beds 16 a and 16 b, regeneration system 10 is capable of being on-board a moving vehicle. An athermal regeneration system refers to the ability of the rapidly oscillating electric field inherent in microwave electromagnetic radiation to transmit energy to polar, or polarizable, molecules sufficient to disrupt the adsorptive forces between that species and the sorbent in the sorbent bed. Typically, harmful impurities, such as sulfur compounds found in fuel, are polar enough to be excited by the oscillating electric field vector of the microwave radiation when adsorbed onto the sorbent. Because microwave energy, rather than thermal energy, is used to regenerate sulfur sorbent beds 16 a and 16 b, regeneration system 10 can be used for mobile use without posing significant risks. Regeneration system 10 is thus capable of producing a hydrogen-rich reformate stream for use in a fuel cell by removing sulfur from fuel. Although FIG. 1 is discussed in the context of using regeneration system 10 to remove sulfur from raw fuel to produce fuel of sufficient purity for use in a fuel cell, regeneration system 10 may be used in any process where it is desired to remove impurities from a fluid, including, but not limited to: desulfurizing liquid fuels such as logistic fuels and gasoline; desulfurizing gaseous fuels such as natural gas (i.e. digester gas, landfill gas, sewage treatment gas, etc.); removing ammonia, amines, and the like from hydrogen in a hydrogen storage system; removing impurities from fuel used in vehicles such as aircraft, submarines, ships, spacecraft, military vehicles, and the like; purifying air in structures such as buildings, tents, safe-havens, and the like; purifying air in vehicles such as aircraft, submarines, ship compartments, spacecraft, military vehicles, and the like; and purifying enclosed areas such as shipping container atmospheres.

Circulation system 12 circulates fuel through regeneration system 10. Piping 40 of circulation system 12 generally includes raw feed line 42, first intermediate line 44, first feed line 44 a, second feed line 44 b, first output line 46 a, second output line 46 b, pure feed line 48, second intermediate line 50, hydrogen line 52, third intermediate line 54, first reverse feed line 54 a, second reverse feed line 54 b, first effluent line 56 a, second effluent line 56 b, contaminated line 58, and discharge line 60.

Raw feed tank 14 contains sulfur-containing fuel and can contain approximately 3,000 parts per million (ppm) sulfur. While vehicles can operate on sulfur-rich fuel, fuel cells require a more hydrogen-pure fuel. Thus, in order to produce hydrogen-pure fuel, the fuel in raw feed tank 14 is pumped by desulfurizer feed pump 16 from raw feed tank 14 though raw feed line 42 to first and second raw feed valves 32 a and 32 b. When first raw feed valve 32 a is in the open position, fuel from raw feed tank 14 is allowed to flow through first raw feed line 44 a and enter first sorbent bed 18 a for desulfurization. Likewise, when second raw feed valve 32 b is in the open position, fuel from raw feed tank 14 is allowed to flow through second raw feed line 44 b and enter second sorbent bed 18 b for desulfurization. When either of raw feed valves 32 a and 32 b is closed, fuel cannot enter the respective sorbent bed. Typically, only one of raw feed valves 32 a and 32 b is open at a time.

First and second sorbent beds 18 a and 18 b are used in alternation, with one sorbent bed being used to desulfurize the fuel while the other sorbent bed is simultaneously being regenerated. For ease of discussion, first sorbent bed 18 a will be discussed when it is being used to adsorb sulfur-containing molecules from the fuel and second sorbent bed 18 b will be discussed when it has reached its breakthrough point and is being regenerated. However, it should be noted that the same discussion would hold true when first sorbent bed 18 a is being regenerated and second sorbent bed 18 b is being used to desulfurize the fuel by simply reversing the direction of each of the valves.

First sulfur sorbent bed 18 a is a layered bed having specially engineered microwave waveguides and containing sorbents for adsorbing sulfur-containing molecules from the fuel supplied from raw feed tank 14. In one embodiment, first sorbent bed 18 a uses a first sorbent and a second sorbent to adsorb sulfur from the sulfur-rich fuel flowing through first sorbent bed 18 a. The first sorbent functions as a presorbent while the second sorbent actually adsorbs the sulfur. The first sorbent acts to protect the second sorbent from dissolved wax, polar nitrogen compounds, and other species that might consume the capability of the second sorbent to remove sulfur from the fuel. The second sorbent is a nano-crystalline, high surface area, large pore, tailor-mixed metal oxide support loaded with a very high dispersion metal, mixed metal clusters, metal compounds, and the like, similar to those described in U.S. Patent Application No. 2003/235,526. It is critical that the second sorbent forms a bond to the sulfur that is strong enough to remove it from the fuel, but weak enough to sufficiently excite the sulfur by the application of a microwave field to desorb from the second sorbent. The microwave field emits electro-magnetic energy sufficient to disrupt the adsorptive forces between the sulfur and the sorbents. The sorbents are chosen to optimize microwave permitivity and minimize direct microwave heating of the sorbent structure and are capable of reducing the amount of sulfur in the fuel so that the desulfurized fuel leaving first sorbent bed 18 a typically contains less than approximately 15 ppm sulfur. In one embodiment, the first sorbent can include Selexsorb CDX, available from Almatis AC Incorporated, Houston, Tex.

In a second embodiment, first sorbent bed 18 a uses an additional sorbent between the first and second sorbent layers of the first embodiments. Thus, a first, second, and third sorbent are used to adsorb sulfur from the sulfur-rich fuel flowing through first sorbent bed 18 a. The first sorbent functions as a presorbent while the second and third sorbents actually adsorb the sulfur. Similar to the first embodiment, the first sorbent acts to protect the second sorbent from dissolved wax, polar nitrogen compounds, water, and other species that might consume the capability of the second sorbent to remove sulfur from the fuel. The second sorbent is designed to adsorb bulky sulfur compounds while the third sorbent is designed as a high capacity selective sulfur sorbent.

First sorbent bed 18 a continues to adsorb the sulfur-containing molecules from the fuel supplied by raw feed tank 14 until first sorbent bed 18 a approaches its breakthrough point. The breakthrough point is the point at which the sorbent bed reaches saturation and cannot adsorb any more sulfur without the adsorbed sulfur breaking through the sorbent bed. The breakthrough point of first sorbent bed 18 a can be monitored by any method known in the art, including, but not limited to: time, flow, fuel sulfur level, or any combination thereof. When first sorbent bed 18 a approaches its breakthrough point, flow through first sorbent bed 18 a is stopped. In one embodiment, first sorbent bed 18 a may also be temperature controlled.

Second sulfur sorbent bed 18 b functions in the same manner as first sorbent bed 18 a and works in tandem with first sorbent bed 18 a. When first sorbent bed 18 a reaches its breakthrough point and needs to be regenerated, the sulfur-rich fuel is redirected through second sorbent bed 18 b for desulfurization while the sulfur-containing molecules in first sorbent bed 18 a are being desorbed and first sorbent bed 18 a is being regenerated. Likewise, when second sorbent bed 18 b reaches its breakthrough point and needs to be regenerated, the sulfur-rich fuel is redirected through first sorbent bed 18 a for desulfurization while the sulfur-containing molecules in second sorbent bed 18 b are being desorbed and second sorbent bed 18 b is being regenerated.

Once the sulfur has been removed from the fuel in first sorbent bed 18 a, the desulfurized fuel leaves first sorbent bed 18 a through first output line 46 a to first output valve 34 a. When fuel is being passed through first sorbent bed 18 a for desulfurization, first output valve 34 a is in the open position and allows the purified fuel to flow through pure fuel line 48 to be collected in purified product tank 20. The desulfurized fuel is then pumped from purified product tank 20 through second intermediate line 50 by purified product pump 22. A first portion of the desulfurized fuel is pumped through hydrogen line 52 to reformer 24 for use. A second portion of the desulfurized fuel continues to be pumped through second intermediate line 50 by desulfurizer recycle pump 26 to third intermediate line 54.

The first portion of the desulfurized fuel is transported to a fuel cell where it is used to produce electricity. Alternatively, the first portion of the desulfurized fuel can be transported to a fuel processor prior to entering the fuel cell. An example of a fuel processor is reformer 24. Reformer 24 can be, for example, a catalytic partial oxidation reformer (CPO). CPO reformers are compact, fuel flexible type reformers having very fast reaction kinetics and correspondingly high space velocities. While these advantages are at the expense of efficiency, the efficiency losses are moderate when used with a solid oxide fuel cell (SOFC) system due to the ability of SOFCs to consume both carbon monoxide and hydrogen. CPO reformers typically begin to function at approximately 300 degrees Celsius (° C.) but actually operate at temperatures greater than approximately 700° C., for example, between approximately 800° C. and approximately 1200° C. The typical start-up time of a CPO reformer is less than approximately forty minutes. In the absence of preheated air, as in the present invention, a fuel-air mixture could be briefly adjusted, in combination with a variety of ignition approaches, to combust the fuel and produce local heating for the CPO reformer until it reaches a temperature of approximately 300 degrees ° C., at which point the CPO reformer can operate without additional combustion.

The second portion of the desulfurized fuel is sent through third intermediate line 54 to first and second reverse flow valves 36 a and 36 b. As mentioned above, for ease of discussion, it is stipulated that fuel is being passed through first sorbent bed 18 a for desulfurization, while fuel is being passed through second sorbent bed 18 b to regenerate second sorbent bed 18 b. Thus, first reverse flow valve 36 a is in the closed position, preventing fuel from entering first sorbent bed, and second reverse flow valve 36 b is in the open position, allowing fuel to enter second sorbent bed 18 b.

When fuel is being passed through second sorbent bed 18 b to regenerate second sorbent bed 18 b, the fuel is passed through in a co-flow or counterflow direction to desorb the sulfur-containing molecules adsorbed on the surface of the sorbent in second sorbent bed 18 b. The dimensions of first and second sorbent beds 18 a and 18 b are determined by the principles of microwave engineering based on the microwave properties of the fuel-filled sorbent at the microwave frequency employed, the properties of the sorbent bed walls, whether the sorbent bed is grounded or electrically isolated, and other factors. To reduce potential damage to second sorbent bed 18 b, the direct exposure of the sorbents in second sorbent bed 18 b to microwave heating is minimized by applying the microwave field from microwave energy source 28 to second sorbent bed 18 b such that second sorbent bed 18 b is effectively subjected to a traveling microwave electric field while still maximizing the penetration of the oscillating microwave electric field onto the sorbent. When the proper microwave frequency range from microwave energy source 28 is applied to second sorbent bed 18 b, the oscillating electric field causes the sulfur-containing molecules to become excited and gain the activation energy necessary to disrupt the adsorptive forces between the impurity, such as the sulfur-containing molecules, and the sorbent. The nature of this excitation provides the activation energy necessary for the polar molecules to desorb from the sorbent. The rate of desorption is calculated by the following equation:

Desorption rate=Ae ^(−ΔG*/RT)

Where A is a constant that contains the number of sites; ΔG* is the free energy of activation of the desorption reaction; R is the gas constant; and T is the temperature in ° K.

Because the impurity adsorbed on the sorbent interacts more strongly with the microwave energy than the sorbent or the fuel, the athermal microwave effect causes the sulfur-containing molecules to be desorbed into the desulfurized fuel passing through second sorbent bed 18 b. The sulfur-containing molecules can thus be flushed away from the sorbent by the desulfurized fuel flowing through second sorbent bed 18 b. Regeneration system 10 thus uses microwave energy, rather than thermal energy to regenerate first and second sorbent beds 18 a and 18 b. After the sulfur-containing molecules have been desorbed into the fuel, the now sulfur-enriched fuel is sent to second effluent valve 38 b. When second effluent valve 38 b is in the open position, the sulfur-enriched fuel is allowed to pass through contaminated line 58 to effluent tank 30. The fuel in effluent tank 30 can then be sent through discharge line 60 to a source that can operate on sulfur-rich fuel, such as a vehicle.

Although FIG. 1 depicts using eight valves to control the flow of fuel through circulation system 12, any number of valves can be used without departing from the intended scope of the invention. For example, a first three-way valve can be used in place of first and second raw feed valves 32 a and 32 b, a second three-way valve can be used in place of first and second output valves 34 a and 34 b, a third three-way valve can be used in place of first and second reverse flow valves 36 a and 36 b, and a fourth three-way valve can be used in place of first and second effluent valves 38 a and 38 b. Alternatively, any combination of valves can be used in regeneration system 10 as long as the flow of fuel can be controlled through circulation system 12. Additionally, although FIG. 1 depicts using two sulfur sorbent beds in alteration, only one sorbent bed may be used in regeneration system 10. If only one sorbent bed is used, the flow of sulfur-containing fuel through the sorbent bed is stopped when the sorbent bed reaches breakthrough, and a flow of desulfurized fuel is sent through the sorbent bed in either a co-flow or counterflow direction while microwave energy is being applied to the sorbent.

Optionally, regeneration system 10 can also include raw feed sensor 62, first sorbent bed sensor 64, and second sorbent bed sensor 64 b. Raw feed sensor 62 is positioned at first intermediate line 44 and detects the flow rate of the fuel from raw feed tank 14. Raw feed sensor 62 can also be designed to detect the concentration of one or more contaminants or constituents of the fuel. First sorbent bed sensor 64 a is positioned at first reverse flow line 54 a. Second sorbent bed sensor 64 b is positioned at second reverse flow line 54 b. First and second sorbent bed sensors 64 a and 64 b sense the flow rate and direction of the output leaving first and second sorbent beds 18 a and 18 b, respectively. Optionally, first and second sorbent bed sensors 64 a and 64 b can also be designed to detect one or more contaminants or constituents in the output. Regeneration system 10 can be designed such that first sorbent bed sensor 64 a must sense a flow in a desired direction into first sorbent bed 18 a in order to activate microwave energy source 28 and similarly, that second sorbent bed sensor 64 b must sense a flow in a desired direction into second sorbent bed 18 b in order to activate microwave energy source 28.

To better illustrate the capability of using microwave energy to regenerate the sorbent beds, FIGS. 2A and 2B show graphs representing the capacity of the sorbents to adsorb sulfur-containing molecules from fuel at the point of initial breakthrough A and at a subsequent breakthough point after microwave energy regeneration B, respectively. In operation, the capacity of the sorbents to adsorb sulfur-containing compounds from the fuel is based on the weight saturation of the sorbents (W_(sat)), which is determined by the following equation:

W _(sat)=[(Sulfur flow rate×weight of sulfur adsorbed by bed)/cross-sectional area of bed]/(bed length×density of sorbent in bed)

As can be seen in FIGS. 2A and 2B, the sorbents were able to remove sulfur from the fuel at approximately the same capacity at the initial breakthrough point A as at subsequent breakthrough point B. At the point of initial breakthough A, W_(sat) was approximately 9.9×10⁻⁴ grams of sulfur per gram of sorbent (gS/g sorbent). At the point of breakthrough after the sorbent bed was regenerated using microwave energy B, occurring after approximately 140 minutes, W_(sat) was approximately 1.8×10⁻³ gS/g sorbent.

FIGS. 3A, 3B, and 3C show a schematic diagram of a second embodiment of simulated moving bed regeneration system 100 having multiple sorbent beds. Regeneration system 100 takes into account the limitation of microwave irradiation penetration depth of packed sorbent beds and generally includes circulation system 102, raw feed supply 104, clean product supply 106, regeneration fuel supply 108, concentrate by-product supply 110, first sorbent bed 112 a having first microwave generator 114 a, second sorbent bed 112 b having second microwave generator 114 b, third sorbent bed 112 c having third microwave generator 114 c, and microwave source 116. Regeneration system 100 also includes a plurality of valves connected to first, second, and third sorbent beds 112 a-112 c, respectively: raw feed valves 118 a, 118 b, and 118 c; reverse flow valves 120 a, 120 b, and 120 c; purified product valves 122 a, 122 b, and 122 c; effluent valves 124 a, 124 b, 124 c; and intermediate valves 126 a, 126 b, and 126 c. Regeneration system 100 interacts and functions in the same manner as regeneration system 10. Similar to regeneration system 10, all of the valves are switchable between an open position and a closed position. In the open position, the valve allows fluid to flow through the valve. In the closed position, the valve prevents fluid from flowing through the valve.

Circulation system 102 circulates fuel through regeneration system 100 and generally includes raw feed line 128, first feed lines 128 a, 128 b, and 128 c, regeneration feed line 130, second feed lines 130 a, 130 b, and 130 c, purified product line 132, product output lines 132 a, 132 b, and 132 c, concentrate by-product line 134, concentrate output lines 134 a, 134 b, and 134 c, recycle line 136, first intermediate line 138 a, second intermediate line 138 b, concentrate output lines 140 a, 140 b, and 140 c, and energy lines 142 a, 142 b, and 142 c. In FIGS. 3A-3C, solid feed lines indicate that the connecting valve is in the open position, allowing fluid flow, and dotted feed lines indicate that the connecting valve is in the closed position, preventing fluid flow.

FIG. 3A shows regeneration system 100 at initial time T_(initial). In operation, first sorbent bed 112 a is initially adsorbing the sulfur from the fuel, second sorbent bed 112 b is polishing, and third sorbent bed 112 c is regenerating. In order for first sorbent bed 112 a to absorb sulfur from raw feed supply 128, raw feed valve 118 a of first sorbent bed 112 a is in the open position, allowing raw feed to enter first sorbent bed 112 a through first feed line 128 a. Raw feed valves 118 b and 118 c of second and third sorbent beds 112 b and 112 c are in the closed position. After the sulfur is adsorbed from the fuel in first sorbent bed 112 a, the purified fuel leaves first sorbent bed 112 a through concentrate output line 134 a and passes through first intermediate valve 126 a to first intermediate line 138 a, which leads into second sorbent bed 112 b. Because second sorbent bed 112 b is polishing, the fluid flows through second sorbent bed with higher purity, and leaves through product output line 132 b. Purified product valve 122 b is open and allows the purified fuel to flow to purified product line 132.

At T_(initial), third sorbent bed 112 c is saturated and must be regenerated. Microwave generator 114 c of third sorbent bed 112 c receives microwave energy from microwave source 116 through third energy line 142 c. Simultaneously, regeneration fuel is sent through product output line 132 c and reverse flow valve 120 c, which is in the open position. The regeneration fuel is sent through third sorbent bed 112 c to regenerate the sorbents in third sorbent bed 112 c. The concentrate then leaves from third sorbent bed 112 c through concentrate output line 134 c and passes through effluent valve 124 c to concentrate by-product line 134. Intermediate valve 126 c is in the closed position. Microwave generators 114 a-114 c can either be powered on continuously or pulsing.

FIG. 3B shows regeneration system 100 when first sorbent bed 112 a is near saturation and needs regenerating and second sorbent bed 112 b has reached its breakthrough point. When first sorbent bed 112 a is fully saturated, T_(initial)+T_(cycle), first feed valve 118 a is switched to the closed position and second feed valve 118 b is switched to the open position so that fuel is allowed to flow from raw feed line 128 through second feed line 128 b to second sorbent bed 112 b but is no longer allowed to flow into first sorbent bed 112 a. The fuel thus flows through second sorbent bed 112 b, where sulfur continues being absorbed into the sorbent to purify the fuel. The partially purified fuel then leaves second sorbent bed 112 b through concentrate output line 134 b, passes through second intermediate valve 126 b, and flows through second intermediate line 138 b into third sorbent bed 112 c, which is fully regenerated and in polishing mode. The purified fuel thus flows through third sorbent bed 112 c polished to get the desired purity and leaves at product output line 132 c, passes through purified product valve 122 c, and into purified product line 132.

To regenerate first sorbent bed 112 a, microwave energy is sent from microwave source 116 through energy line 142 a to first microwave generator 114 a connected to first sorbent bed 112 a. At the same time, regeneration fuel from regeneration feed line 130 is sent through second feed line 130 a and reverse flow valve 120 a, which is in the open position. The regeneration fuel is used in combination with the microwave energy from microwave generator 114 a to desorb the sulfur from first sorbent bed 112 a. The partially purified fuel then leaves first sorbent bed 112 a through concentrate output line 134 a. Effluent valve 124 a is in the open position and allows the effluent to flow through first output line 140 a to concentrate by-product line 134.

FIG. 3C shows regeneration system 100 when second sorbent bed 112 b is near saturation and needs regenerating and third sorbent bed 112 c has reached its breakthrough point. When second sorbent bed 112 b is saturated, T_(initial)+2T_(cycle), second feed valve 118 b is switched to the closed position and third feed valve 118 c is switched to the open position so that fuel is allowed to flow from raw feed line 128 through first feed line 128 c to third sorbent bed 112 c but is no longer allowed to flow into second sorbent bed 112 b. The fuel thus flows through third sorbent bed 112 c, where sulfur continues being absorbed into the sorbent to purify the fuel. The partially purified fuel then leaves third sorbent bed 112 c through concentrate output line 134 c and third intermediate valve 126 c into recycle line 136 to first sorbent bed 112 a, which is in polishing mode. The partially purified fuel thus flows through first sorbent bed 112 a polished to the desired purity and leaves at product output line 132 a, passes through purified product valve 122 a, and into purified product line 132.

To regenerate second sorbent bed 112 b, microwave energy is sent from microwave source 116 through energy line 142 b to second microwave generator 114 b connected to second sorbent bed 112 b. At the same time, regeneration fuel from regeneration fuel line 130 is sent through second feed line 130 b and reverse flow valve 120 b, which is in the open position. The regeneration fuel is used in combination with the microwave energy from microwave generator 114 b to desorb the sulfur from second sorbent bed 112 b. The effluent then leaves second sorbent bed 112 b through concentrate output line 134 b. Effluent valve 124 b is in the open position and allows the effluent to flow through second output line 140 b to concentrate by-product line 134.

FIGS. 4A-4C show regeneration system 100 at initial time T_(initial), after first sorbent bed 112 a is saturated, and after second sorbent bed 112 b is saturated, respectively, using reverse flow regeneration. Reverse flow regeneration is typically used if sorbent beds 112 a-112 c are layered beds. Regeneration system 100 functions the same as when reverse flow regeneration is not used, except that regeneration fuel is fed to sorbent beds 112 a-112 c through second feed lines 130 a-130 c and effluent fuel is removed from sorbent beds 112 a-112 c through output lines 140 a-140 c.

The regeneration system of the present invention purifies fluids and athermally regenerates sorbent beds. For example, the regeneration system can be used to absorb impurities such as sulfur from a raw feed fuel. The regeneration system can be used in any process where it is desired to remove impurities from a fluid. One or more sorbent beds are used to adsorb one or more classes of impurities from a fluid. When a sorbent bed approaches capacity, or its breakthrough point, a fluid stream containing a low level of the impurity is used in conjunction with electromagnetic radiation to desorb the impurities from the sorbent bed and carry them away in the fluid stream. With the impurities removed from the sorbent bed, the sorbent bed is regenerated and ready for reuse. Microwave radiation is particularly effective in removing the impurities from the sorbent bed when the fluid to be purified, the fluid used to carry away the impurities, and the sorbents have a relatively weak interaction with the frequency of radiation used compared to the impurity-sorbent adduct. In addition, the use of microwave energy allows the regeneration system to safely be used on-board a vehicle.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 

1. A method for regenerating at least one impurity-adsorbing sorbent bed, the method comprising: a) passing impurity-containing fluid through the impurity-adsorbing sorbent bed, the impurity-containing fluid containing an impurity; b) adsorbing the impurity in the impurity-containing fluid with the impurity-adsorbing sorbent bed to produce a purified fluid; c) sending a portion of the purified fluid back through the impurity-adsorbing sorbent bed that contains the impurity adsorbed in step b; and d) exposing the impurity-adsorbing sorbent bed of step c to microwave energy to desorb the impurity adsorbed on the impurity-adsorbing sorbent bed.
 2. The method of claim 1, wherein sending the portion of the purified fluid through the impurity-adsorbing sorbent bed occurs after the impurity-adsorbing sorbent bed reaches a breakthrough point.
 3. The method of claim 1, wherein passing the impurity-containing fluid through the impurity-adsorbing sorbent bed and sending the portion of the purified fluid through the impurity-adsorbing sorbent bed occur independently of each other.
 4. The method of claim 1, wherein exposing the impurity-adsorbing sorbent bed of step c to microwave energy comprises providing electro-magnetic energy sufficient to disrupt adsorptive forces between the impurity-adsorbing sorbent bed and the impurity.
 5. The method of claim 1, wherein desorbing the impurity comprises desorbing the impurity into the portion of the purified fluid.
 6. The method of claim 1, wherein the purified fluid has an impurity concentration of less than 15 parts per million by weight of the impurity.
 7. The method of claim 6, and further comprising feeding a second portion of the purified fluid into a fuel cell to produce electrical energy.
 8. The method of claim 1, wherein the impurity-adsorbing sorbent bed is an athermal impurity-adsorbing sorbent bed, and wherein exposing the impurity-adsorbing sorbent bed of step c to microwave energy comprises athermally regenerating the impurity-adsorbing sorbent bed of step c.
 9. A method for regenerating an impurity-adsorbing sorbent bed, the method comprising: passing impurity-containing fluid through a first impurity-adsorbing sorbent bed, the impurity-containing fluid containing an impurity; adsorbing the impurity in the impurity-containing fluid with the first impurity-adsorbing sorbent bed to produce a purified fluid from the first impurity-adsorbing sorbent bed; sending a portion of the purified fluid from the first impurity-adsorbing sorbent bed through a second impurity-adsorbing sorbent bed that contains the impurity; and exposing the second impurity-adsorbing sorbent bed to microwave energy to desorb the impurity.
 10. The method of claim 9, wherein exposing the second impurity-adsorbing sorbent bed to microwave energy comprises providing electro-magnetic energy sufficient to disrupt adsorptive forces between the second impurity-adsorbing sorbent bed and the impurity.
 11. The method of claim 9, wherein desorbing the impurity comprises desorbing the impurity into the portion of the purified fluid from the first impurity-adsorbing sorbent bed.
 12. The method of claim 9, wherein the purified fluid from the first impurity-adsorbing sorbent bed has an impurity concentration of less than 15 parts per million by weight of the impurity.
 13. The method of claim 12, and further comprising feeding a second portion of the purified fluid from the first impurity-adsorbing sorbent bed into a fuel cell to produce electrical energy.
 14. The method of claim 13, and further comprising feeding the second portion of the purified fluid from the first impurity-adsorbing sorbent bed to a reformer prior to feeding the second portion of the purified fluid from the first impurity-adsorbing sorbent bed into the fuel cell.
 15. The method of claim 9, wherein the first and second impurity-adsorbing sorbent beds are first and second athermal impurity-adsorbing sorbent beds, and wherein exposing the second impurity-adsorbing sorbent bed to microwave energy comprises athermally regenerating the second impurity-adsorbing sorbent bed.
 16. The method of claim 9, and further comprising: passing the impurity-containing fluid through the second impurity-adsorbing sorbent bed; adsorbing the impurity in the impurity-containing fluid with the second impurity-adsorbing sorbent bed to produce a purified fluid from the second impurity-adsorbing sorbent bed; sending a portion of the purified fluid from the second impurity-adsorbing sorbent bed through the first impurity-adsorbing sorbent bed that contains the impurity; and exposing the first impurity-adsorbing sorbent bed to microwave energy to desorb the impurity.
 17. The method of claim 16, wherein the impurity-containing fluid is passed through the second impurity-adsorbing sorbent bed after the first impurity-adsorbing sorbent bed reaches a breakthrough point.
 18. The method of claim 16, wherein the first and second impurity-adsorbing sorbent beds are first and second athermal impurity-adsorbing sorbent beds, and wherein exposing the second impurity-adsorbing sorbent bed to microwave energy comprises athermally regenerating the second impurity-adsorbing sorbent bed, and wherein exposing the first impurity-adsorbing sorbent bed to microwave energy comprises athermally regenerating the first impurity-adsorbing sorbent bed.
 19. The method of claim 16, wherein desorbing the impurity comprises desorbing the impurity into the portion of the purified fluid from the second impurity-adsorbing sorbent bed.
 20. The method of claim 16, and further comprising feeding a second portion of the purified fluid from the second impurity-adsorbing sorbent bed into a fuel cell to produce electrical energy. 